Romney, who will become the Republican presidential nominee this week during the GOP convention in Florida, said he was joking last week when he told a Michigan crowd "no one's ever asked to see my birth certificate" against a backdrop of the so-called birther movement questioning President Obama's citizenship.

"I think if he had to do it over again, he wouldn't make the joke," Christie said Tuesday on NBC's "Today" show. "But you know what, when you're on camera 12, 14 hours a day, and you're at a big rallies and you're just going off the cuff, there are going to be times you're going to say stuff you wish you could take back. If you get a chance to talk to Governor Romney, I think he'd tell you that he wishes he could take that one back."

Christie is a keynote speaker at this week's Republican National Convention in Tampa.

Christie also denied a New York Post article published Monday saying he declined to accept a vice presidential nomination because he does not think Romney can win on Election Day, NBC said.

"It's just complete garbage," Christie said. "The two reporters that wrote the story know me and have my phone number and neither of them ever called me to ask me about the story, to verify or debunk it. They just wanted to put something on the front page on the day [of the GOP convention] was canceled. So I'm telling you [the story is] categorically, absolutely untrue."

He told NBC he had worked for Romney for nearly a year and "I absolutely believe he can win and will win."

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